The present invention relates to a positive-working, radiation-sensitive mixture, and more particularly to such a mixture which is rendered soluble by irradiation, and which contains as the essential constituents,
(a) a compound having at least one C--O--C bond which can be split by acid,
(b) a compound which forms a strong acid when irradiated, and
(c) a binder which is insoluble in water and soluble in aqueous-alkaline solutions. A mixture of this type is suitable for the preparation of printing plates and photoresists. Mixtures comprised of these basic constituents are described, for example, in U.S. Pat. No. 3,779,778, No. 4,101,323 and No. 4,189,323, in German Offenlegungsschriften Nos. 27 18 254 and No. 29 28 636 and in published European Patent Applications Nos. 0,006,626 and 0,006,627.
Although it is mentioned in these printed publications that other polymeric substances can also be added in addition to the alkali-soluble binders, nevertheless, alkali-soluble binders, in particular phenolic resin novolaks, are described virtually exclusively in the illustrative examples.
Other binders or resins are, however, already known as additives for positive-working radiation-sensitive or light-sensitive mixtures based on o-quinone-diazides. Thus, German Pat. No. 16 22 301 describes the addition of polyvinyl alkyl ethers, German Offenlegungsschrift No. 22 36 941 describes the addition of acrylic resins, German Offenlegungschrift No. 27 33 267 describes the addition of terpene resins and German Offenlegungschrift No. 26 17 088 describes the addition of reaction products of organic isocyanates with novolaks to o-quinone-diazide layers, which additionally can contain alkali-soluble novolaks.
In spite of the numerous proposals, some of which were made a considerable time ago, for the improvement and modification of the properties of positive-working light-sensitive layers based on o-quinone-diazides for the most diverse applications, these layers still do not yet meet all the requirements.
Specifically, in the case of positive photoresist compositions for micro-electronic applications, where a high resolution and exact line definition, even after baking steps, are of particular importance, resin additions of the types mentioned have been unable to gain acceptance. Even polyvinyl alkyl ethers are still not used very widely, in spite of numerous efforts in microelectronics to introduce resists containing these additives into the mass production of chips. A main obstacle appears to be the fact that disadvantages, for example, a loss of sharpness after baking, can arise in diazo layers after the addition of these resins during certain working steps under production conditions.